The Best Choices for Your First Solar Battery Bank

You will make a lot of mistakes in the beginning of your “off grid” adventures and your batteries will pay the price whether they are deluxe and expensive models or decent quality and cost effective.

If your solar installer/designer tries to sell you a “high end” (and very expensive) battery bank for your first energy system it might be an indication he/she does not have enough experience or is more concerned about profit margins than what is right for you.

It is a shame to spend 10 to 20 thousand dollars (ore more) on a battery bank that will likely not last half the time it was designed for.

Once you destroy your first set (which almost everyone does), you will be ready to invest in a better quality bank.

Here we will discuss the best options when designing a battery bank for someone who has never lived off the power grid before.

A new set of T105s should last 4-6 years if looked after (according to what is taught in this article) in a well designed solar electric system. We have used them for up to 8 years before replacing, although the last few months were not great. If abused and treated poorly, they will last about 1-2 years.

TROJAN L16s 370 AMP HOURS AT 6 VOLT

The better choice for your first bank of batteries is the Trojan L16. They have about 60% more capacity but cost more than double. The reason for the extra cost is they have far more lead and electrolyte than the T105, making them last a lot lot longer.

The usual price for a Trojan L16 is approximately $270-320 USD each. The price is typically closer to $270 when buying in bulk.

The L16 is a great battery for many solar systems as they are well made, have a decent amount of lead and electrolyte and they are a manageable size and weight for transporting. Although we highly recommend them for new off gridders, we also recommend them for experienced solar homesteaders as well. In fact they are what we are using for our main battery bank right now.

Here are the numbers for the Trojan L16 if you were to install one string in your battery bank:

A new set of Trojan L16s should last about 6-9 years if well taken care of. We have seen them used up to 12 years and as little as 4 years. Battery care is very important.

SURRETTE S460 350 AMP HOURS AT 6 VOLTS

Another good choice for the solar newbie is the S460 by Surrette. You may have already assumed the S460 would be a 460 AH battery but it is not. It’s C20 AH rating is 350. It’s C100 rating is 460. What’s the difference?

Regardless of the misleading AH rating, the S460 is a well built battery. They are made in Nova Scotia Canada and are usually of the best quality.

The usual price for a Surrette S460 is approximately $300-400 USD each.

They are made specifically for solar electric systems and were originally based on the L16.

Here are the numbers for the Surrette S460 if you were to install one string in your battery bank:

SURRETTE S530 400 AMP HOURS AT 6 VOLTS

The Surrette S530 looks exactly like the S460 but it does contain more lead and more capacity. As it is in the exact same container as the S460 the extra lead means less room for electrolyte. Some would argue that adding more lead and less electrolyte could be a problem but it should be mentioned that Surrette actually increased the size of the battery’s case a few years ago when they added a new model…the S600. It even has more lead but right now we are talking about the S530.

The S530 is a well built 400 amp hour 6 volt battery. They are made in Nova Scotia Canada and are a high quality battery.

The usual price for a Surrette S530 is approximately $350-450 USD each.

They are made specifically for solar electric systems and were originally based on the L16. They started with the basic shape and size of an L16 but made it bigger and stronger using thicker lead plates. If you can get a good price when buying the S530, they are a good choice as well for the solar first timer.

Here are the numbers for the Surrette S530 if you were to install one string in your battery bank:

When buying your first set of batteries it can be intimidating to say the least. There are so many choices. Many times the decision will be made for you as you might only be able to get one brand of batteries in your location.

It is likely that Trojan will be available and cost effective in your area as they are one of the biggest solar battery suppliers on earth. If you really want Surrette S530s but find out that you will have to pay much more for them compared to a Trojan or other brand L16, the non Surrette is the better choice.

Another consideration is availability and lead times for warranty issues. As nice as Surrette batteries are, they are rarely readily available. When we operated a solar store, it was not uncommon to have a six to nine month lead time when buying directly from Surrette. We were not a small battery dealer either. We regularly bought pallets and pallets of batteries. Prepaying for 6 pallets of S460s and waiting for nine months is very hard way to do business.

If you will have to wait a few months for your battery bank, what will happen if there is a warranty issue?

Are you prepared to wait three to six months to get a replacement for your defective battery?

If not, you better buy what the local battery supplier keeps in stock.

What about other brands of the golf cart battery or L16s?

While Trojan is responsible for putting the golf cart battery and the L16 in the spotlight, there are hundreds of other battery manufactures that make good quality batteries. Some decent names are US Battery, Interstate, Energizer, Deka, Centennial, Universal and Exide. Most golf cart batteries are of reasonable quality. When looking at other brands of golf cart batteries make sure they are in fact 220-230 AH 6 volt batteries and weigh between 60 and 70 pounds. There are lower amp hour golf cart batteries out there that will not provide the capacity you are looking for.

The L16 is a little more complicated to compare. There are many shapes and sizes of L16. They can vary from 200 AH to 400 AH. If you are purchasing some L16s make sure they are in the range of 320 to 400 AH and they weigh approximately 100 to 125 pounds. Most folks don’t realize that even Trojan has many models of L16 that vary from 370 to 435 AH (C20) and weigh between 100 and 125 lbs.

If you can find a golf cart or L16 battery that is made by a known battery manufacturer, and they are readily available and affordable, they are probably a good choice. The importance of having a battery that is readily available cannot be understated. If you have a problem with one or more of your batteries, you will not be able to wait months for a replacement.

Why are you only recommending batteries Flooded Lead Acid (FLA) batteries?

For your first (and probably all) battery banks, flooded lead acid batteries are the best option. Sealed batteries also known as AGM batteries are not very forgiving. Any battery that is sealed cannot be “brought back to life” if you cause any damage by undercharging or overcharging.

With an FLA battery, if you discharge the battery too much and cause a build up of sulfate, you can bring it back to life with an equalization charge. Equalization is a purposely over charging the battery to remove sulfate and mix the electrolyte. However, water will escape and need to be returned. It is easy to add water to an FLA battery but a sealed battery is sealed and cannot take water. If you over charge a sealed battery by mistake (or on purpose), any water that escapes cannot be returned. Learn more about equalization and battery maintenance.

Sealed batteries have their application but they are not usually a good option for the off the grid homestead.

What about used batteries?

This is a request we hear on a daily. Someone knows a guy who can get batteries from a phone or electric company that are being replaced due to regular maintenance. As the story goes, the batteries are like new and just need a new home. This is almost NEVER a good idea.

However these guys seem to know to how to repair old batteries which might be worth looking into?

Phone and electric companies are not stupid. They do not spend money on new batteries because it is fun. They spend money on new batteries as they know the old batteries are worn out. And 99% of the time they are worn out. I hate to see folks spend their hard earned money on junk. Most of the time these companies are thrilled to see you come along with your money and your truck. Discarding batteries is very expensive. You assume that responsibility when you take the used batteries away. Please do not ever buy used batteries. If they are free and you can transport them for free, then it might be OK. Other than that situation, do not waste your time with used batteries.

I can get a whole bunch of 12 volt car batteries for a good price. Will they work?

Absolutely not. Car batteries or starting batteries are not suitable for deep cycle applications. Batteries that are made to start a car engine are made with a lot of very thin plates (to provide a lot of surface area) that provide good surge power, but they will not work as a deep cycle battery. The plates are paper thin.

The average car starting battery is good for about 10 cycles. If you leave your headlights on and drain your battery more than 5 or 10 times, it will be destroyed. The plates will either get hot and warp or be eroded and end up sitting on the bottom of the battery. Deep cycle batteries use much thick plates made to handle deep cycles.

What about 12 volt deep cycle batteries?

Unfortunately, 12 volt “deep cycle”/”marine” batteries do not make sense for the majority of off grid applications. If you imagine a 6 volt golf cart battery, it is composed of 3 – two volt cells that are wired in series to make six volts. There is just enough space to make fairly thick lead plates and fit them in the battery case. Now try and fit 6 – two volt cells in the same size container as in the average “deep cycle” 12 volt battery. There is simply not enough space to do it right.

As a general rule the lower the battery voltage, the better the battery will be for deep cycling. The truth is most 12 volt so called “deep cycle” batteries are not really deep cycle at all. They are really just starting batteries with plates that are a little bit thicker. The term “marine battery” also refers to a starting battery that has plates that are slightly thicker than a starting battery.

The photo below shows the result of deep cycling a 12 volt “marine”/”deep cycle” battery. Note the badly warped plates. They cannot handle the heat generated during hard deep cycling as would be common in most solar homes.

The only time we would recommend 12 volt batteries would be for a tiny system that you do not have to rely on. Maybe you have a cottage and you only want a small system to operate a few LEDs and a radio. In this case a 12 volt deep cycle battery would probably be fine. Another 12 volt battery application would be a solar traffic light or sign light. While a real deep cycle 2, 4, or 6 volt battery would perform much better, an inexpensive 12 volt unit might be OK for small systems.

Great article! It was very detailed but also understandable. It’s so helpful for this newbie who doesn’t want to put out the dough for AGM or Lithium but still wants a great battery. I really don’t want to invest in a lot of expensive batteries when I know that I’m going to make mistakes and not give it the attention it probably needs at this point. I have 4x100W solar panels for my 27ft travel trailer. Do you think that one Trojan T105 will work or should I buy a different battery or more than one? Any advice for me?

Hi and thanks very much for your info! I’m a noob and starting to setup my own off-grid solar setup. I have picked up 4 100 AH solar style batteries (all same make) and looking at adding a separate string of 6-8 of the Trojan T105’s to run in a separate string, being able to split the strings, so that I can run the smaller string for the smaller household items, then use the larger string (the 6-8 T105’s) to handle things like the refrigerator and larger items.

I am looking at solar panels now having around 230-250 watts per panel, but unsure how many panels I will need to run each of these banks.

What would you recommend to be the proper amount of panels for each bank (4-100 ah string and 6-8 T105’s string)? I live just south of San Diego, so lots of good sun with mild temps (typical average high year around is about 72-75 degrees).

Thank you for your comment. Since you already have two 100 AH batteries in series adding a 400 AH to them will not work well. When you wire batteries in series all of the batteries will operate to the capacity of the smallest battery in the string. Adding the 400 amp hour battery will work no better than adding a 100 amp battery. The same applies with solar modules. You could have 9 units of 200 watt solar modules at 24 volts in a string. If you add a 50 watt 24 volt module in series with the others, the other 9 modules will only output 50 watts each. Hope this helps…Jody

Hi Jody,
I’m anoob as noon can get, but the last 6 months I have been researching a total off grid system and think I jumped the gun. Meaning I have a 48 volt system on the way, but forgot to get the batteries… AKA didn’t want there $700 for one battery. Love the info you have given which opened my eyes.
So if I’m getting this right I need to find 8x 6 volt golf cart batteries?
Can you tell me what I can get at Menard’s.. Yes I know you are shaking your head…
But I’m on a very tight budget and if I can’t get it at Menard’s I can’t get it till taxes come and again I have a budget of a grand.

I have made good use of used 12 volt agm batteries for over 6 years at a time. I can still buy a 130 ah agm for under $100 after they are removed from a data storage center. I have run a whole house on 24 of them without problem and wouldn’t hesitate to go back to them when my newL-16’s are toast. Don’t think the bigger batteries are so much better now.

Thank you for your comment. You have done really well. Most folks aren’t so lucky (or careful) to be able to make used batteries work that well. Have you been disappointed with the L16s? If so it is probably a good idea to go back to the used AGMs if you can get them from the same reliable supplier. Let me know how you make out when the time comes and enjoy your power system…Jody

Wow. You are my hero. That is really impressive. Thank you for sharing that. What is your secret? Any advice you could share with us? Are you located in the northern part of the world? Thanks so much for your comment. 15 years from a set of Surrette L16s is incredible. We live a few hours from Surrette’s plant and have been impressed with their batteries and manufacturing techniques for awhile. As well they are a major employer in a small town in Nova Scotia, Canada. Thanks again Carl…Jody

What bothers me is I see lot’s of shady solar/alternative sales people. Who don’t wanna do whats best for the customer only whats best for their pocket. Any company with GEL batteries or an over stock will claim they are the best & cheaper in the long run if they need to unload them. Any company who only sells FLA will claim those are the best. It’s really annoying, anytime a customer feels ripped off or taken advantage of, it not only hurts that company but other wind/solar companies as well.

I’m designing a test system for a competition that will need to operate on 2,5 KW AC load for for 24 hrs power by solar PV in the day and batteries at night.
The battery bank will need to be at 0 charge at the beginning of the competition and the load will have to operate on solar in the day (and be able to charge the batteries) so that the batteries can run it for 13 hrs at night.
this competition will be in New Mexico in April where the sun will be 7 hrs (noon sun)

I came up with 16 of the L16 (370 AH) @ 6V ea with 2 strings of 8 for a 48V config
and 6,2 KW PV system system

From your info I will assume the sun shines for 11 hours for a total of 7 sun hours. Then you need to keep the load operational for another 13 hours.

First we need to calculate how much power we need to create with our solar array. You will need to create 2.5 kWhs X 24 hours for a total of 60 kWhs.

Assuming 7 sun hours we can divide 60 kWhs by 7 hours to get the size of our array which will be 8.57 kWhs in a perfect world.

Realizing a 100 watt solar module generates closer to 80 watts I always add 25% making your array size 10.71 kWhs. Solar modules are rated in a lab at 25 degrees Celsius with the “sun” shining at 1000 watts per square meter. Since that rarely happens I always derate. Especially in warmer climates. The hotter the solar module the less power output. That will have to be your decision based on finances etc.

I just don’t see how a 6.2 kW array would do the trick for you unless your battery bank was already full. 6.2 kW array X 7 sun hours = 43.4 kWhs.

Now that we have generated the power, we need to store enough for the remaining 13 hours. 13 hours x 2.5 kWhs = 32.5 kWhs.

As you stated a good L16 will store roughly 370 amp hours at the 20 hour rate. We will be discharging ours a little faster (13 hours) decreasing the capacity of each battery to about 349 AH. Go to http://solarhomestead.com/battery-amp-hour-ratings/ to find more about that. 349 AH x 6 volts = 2.094 kWhs per battery.

32.5 kWhs divided by 2.094 kWhs per battery = 15.5 batteries or 16 realistically to get your 48 volt bank which is exactly what you came up with.

Hope that makes sense. It is pretty much what you had already figured out. Good luck and please don’t hesitate to question me. I make mistakes like everyone else.